A compound of element A and oxygen has a mole ratio of A:O = 2:3. If 8.0 grams of the oxide contains 2.4 grams of the oxygen. What is the atomic weight of A?

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Total mass of oxide = 8.0

Mass of O in the oxide = 2.4

Mass of A in the oxide = 8.0 - 2.4 = 5.6

Moles of O in the oxide:

`mol es = (mass)/(molar mass)`

`= (2.4 grams)/(16.0 (gram)/(mol e)) = 0.15 mol es`

Remember that the ratio of A with O is 2:3 therefore:

2:3 and ?:0.15

`= 0.15 * 2/3 = 0.1 mol es A`

**Molar mass of A:**

`mol es A = (mass A)/(molar mass A)`

`molar mass A= (mass A)/(mol es A)`

`molar mass A= (5.6)/(0.1)`

`molar mass A = 56 (g)/(mol e)`

**Molar mass of the Oxide:**

2:3

`= A_2O_3`

`=56(2) + 16(3)`

`= 160 (g)/(mol e)`

**Sources:**

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